Since the early 1960's, semiconductor wafer manufacturing has relied on step-and-repeat imaging to reproduce circuit patterns rapidly and at low cost. In step-and-repeat photolithography machines, a reticle that has one or a few circuit patterns on it is projected onto the semiconductor wafer through a lens. 4× reduction optics have been the most popular, but reductions of 20×, 10×, 5×, 2× and 1× have been used depending on the application. Even a few magnifying projection machines have been built. A substrate, usually a silicon wafer, is moved in a step-and-repeat manner by an X, Y stage. When the stage stops, a shutter is opened, light passes through the reticle and reduction lens, and the reticle image is quickly transferred to a photosensitive film on the substrate. For nearly 40 years, this method has been the most productive way to replicate Integrated Circuit (IC) chip patterns.
Recently, this step-and-repeat technique for imaging circuit patterns on a substrate has found utility in packaging of high density IC chips. At today's density of interconnect and value for one microprocessor chip, high yield projection methods are replacing contact printing as the photocopying method of choice.